1. Field of the Invention
The present invention relates to photo film cassette containing a photo film. More particulary, the present invention relates to an improvement of photo film cassette of which a leader of the photo film is excited by rotation of a spool in an unwinding direction.
2. Description Related to the Prior Art
There is a type of photo film cassette, of which a leader of unexposed photo film is pre-contained in the cassette shell, and advanced to an outside of the cassette shell when a spool is rotated in an unwinding direction. Such a type of cassette is suggested in U.S. Pat. Nos. 4,832,275, 4,834,306, 4,848,693 (corresponding to JP-A 2-18545), U.S. Pat. No. 5,151,730 (corresponding to JP-A 4-320258), U.S. Pat. No. 5,271,577 (corresponding to JP-A 3-37645), U.S. Pat. Nos. 5,296,887, and 5,407,106 (corresponding to JP-A 3-37645). Also, there is a cartridge for containing a developed photo film having the same structure as the above type, for facilitating the handling and the preservation of the developed photo film, as disclosed in U.S. Pat. No. 5,083,155 (corresponding to JP-A 3-179341).
The spool is constituted of a spool core and two flanges, which are disposed on the spool core, for contact with the ends of a roll of the photo film, to restrain the turns of the photo film. In the cassette of the leader-advancing type, it is necessary to transmit rotation of the spool to the roll of the photo film. To this end, the flanges of the spool are provided with respective ring-like lips formed on their periphery and projected toward one another. The ring-like lips are located to cover edges of the outermost turn of the photo film, and prevent the roll from being loosened.
To advance the leader of the photo film, it is necessary to spread both flanges in the vicinity of a photo film passageway, to release the ring-like lips from regulation. The flanges are rotatable, and are not rotated without being deformed. The flanges are formed with a the small thickness. But the same flanges require sufficient rigidity, resistance to abrasion, and amounts of other characteristics.
To impart adequate characteristics to flanges, such as rigidity and resistance to abrasion, it is necessary to select resin suitably as a raw material. The method of forming the flanges must be also considered in the selection of the resin. There are suggestions of a preferred resin and forming method in U.S. Pat. No. 5,211,348 (corresponding to JP-A 4-251841) and JP-A 6-148808. In those suggestions, a continuous resin sheet of a polyethylene type having a small thickness (0.3 mm) is formed by extrusion. The continuous sheet is thermoformed in a forming step by the vacuum forming or pressure forming. The continuous sheet is punched in a regular shape in a punching step, to form the flanges.
In this method of producing flanges, a continuous sheet of resin is drawn from a sheet roll, is heated in a heating step, and subjected to the vacuum forming or pressure forming in the forming step. The continuous sheet is punched in the punching step, to obtain the flanges. The sheet is withdrawn in a withdrawing step. It is inevitable that a manufacturing system for those steps is large and expensive. The withdrawn sheet after the punching step is surplus remaining as waste of raw material. Also, there is a low precision of sizes of the molded pieces due to the vacuum forming or pressure forming another pieces cannot be formed at a precise desired thickness.
In the known cassette of the leader-advancing type, there is a separator claw formed integrally with the cassette shell. To advance the leader of the photo film to the outside, the separator claw is contacted on an end of the leader during the rotation, separates it from the roll, and directs it to the outside of the cassette shell through the photo film passageway.
To release the photo film from contact with ring-like lips, there are several known structures. In one of the structures, a pair of separator claws are formed to lie in positions along a width of the photo film. Support portions of the separator claws operate to deform part of the ring-like lips in directions away from one another. In another structure, a single separator claw is formed. After the separator claw separates an end of the leader from the roll of the photo film, side edges of the photo film spread the ring-like lips in directions away from one another in partial deformation.
It is inevitable that the photo film has high rigidity. When the photo film is wound in a roll form, the photo film has considerably great force of tending to recover its original straight form. The ring-like lips require resistance to the recovering force of the photo film to prevent the roll of the photo film from being loosened. To avoid deformation or the spreading of ring-like lips, there is a proposal in JP-U 68047 in which a greater thickness is imparted to the ring-like lips for the purpose of reinforcement.
Inside the cassette shell, there is high friction between the outer turns of the photo film and the inside faces of the ring-like lips. The ring-like lips are likely to be rubbed and worn, so that resin powder is created. It is likely that the resin powder exits with the photo film from the cassette shell, contaminates the inside of a camera, and is photographed with an image on the photo film. In view of reducing the friction between the photo film and the ring-like lips, there are documents, such as U.S. Pat. No. 4,848,693 and JP-U 6-68047, proposing flanges of which a ring-like lip has an inside face inclined as viewed in cross section, the inclination being in a direction away from an axis of the spool in accordance with the increase in the height of the ring-like lip.
Having the inclination, the inside face of the ring-like lips is an undercut to be released from a mold, in forming the flanges by the injection molding. It is likely in the injection molding that the undercut of the molded piece fails to be ejected, and if ejected forcibly, cannot resist deformation.
To avoid deformation of ring-like lips against the recovering force of the photo film in the roll form, there is also a suggestion in which ring-like lips are provided with respective ring-like projections, which are formed on their periphery and projected away from a rotational axis of the spool.
As referred to above, the plural known structures may release the photo film from regulation of looseness in contact with ring-like lips. Certainly the leader of the photo film is easy to advance. However, there are shortcomings: the ring-like projections are contacted on the photo film and/or the support portions of the separator claws, and are likely to be rubbed and worn. To reduce friction between the photo film and the ring-like projections, U.S. Pat. No. 4,848,693 proposes flanges of which a ring-like projection has inclination in a direction opposite to a projected direction of the ring-like lip. Namely, the two ring-like projections are inclined to come away from one another in their projected direction around the ring-like lips. The inside faces of the two ring-like projections operate for guiding the photo film into the space between the ring-like lips while the photo film is wound.
While the spool is rotated in the direction of winding the photo film, tension is being applied to the photo film. The photo film passes between the ring-like lips, and is wound about the spool core safely. But without application of the tension to the photo film, there is a problem in that rotation of the spool core causes the photo film to wind the ring-like projections, not on the spool core. The ring-like projections are likely to collapse in such a case. The failure in guiding the photo film into a space between the ring-like lips is remarkably serious when the ring-like projections have a considerably great angle of inclination.
However, the flange producing method in U.S. Pat. No. 5,211,348 and JP-A 6-148808 has a problem in that it is difficult to form the inclination in a tolerable range of a predetermined angle, in view of low precision of the shape of the molded pieces due to the vacuum forming or pressure forming. No suitable inclination can be formed in a range resistant to the collapse in contact with the photo film.
In consideration of forming flanges by the injection molding capable of production at high speed, at large scale and with automation, a mold mark remaining on a molded flange is a problem in that it causes scratches to the photo film and difficulties in the film advancement. The construction of a gate of molds thus requires improvement. With the ring-like lips and ring-like projections formed about the somewhat thin flanges, melted resin flows only slowly to the distal end of the molds. The injection molding is thus likely to cause unwanted creation of short shot and sink marks locally.